The player whose turn was before mine dropped out of the game because he got the same error. A quick search in this forum revealed the last time this was reported the game was abandoned. So I have actually no faith this can get resolved.
It could be a corrupted Civ installation of Player A making the invalid save file on Turn X. Then the garbage data (it may be only 1% of the save file) causes ACCESS_VIOLATION on a correct Civ installation of Player B making his Turn Y.
I see this speculation as lack of save reading validation from Firaxis devs for sure. But, this also might help
Some external way, a tool to validate save files “more”. Don’t know if it exists.
Every player verifies game files, probably re-install Civ. And then 1-2 full Rounds are reverted hoping Turn X wasn’t too far from Turn Y.
So I have actually no faith this can get resolved.
Thank you for your thoughts. The game is actually far advanced and it is clear who is going to win. So I’m not sure if other players in this game want to try to fix this.